16 Marks Questions, Assignment Problems

PART - B (16 Marks Questions)

Anna University Questions:

Intrinsic semiconductor

1. Obtain an expression for intrinsic carrier concentration in an intrinsic semiconductor.

2. Derive an expression for the density of holes in an intrinsic semiconductor.

3. Derive an expression for concentration of holes (absence of electrons) in intrinsic semiconductors.

4. Obtain an expression for the carrier concentration of electrons in an intrinsic semiconductor.

5. Assuming the Fermi Dirac distribution derive an expression for the concentration of electrons per unit volume in the conduction band of an intrinsic semiconductor. 

Extrinsic semiconductors

6. Derive the relation for carrier concentration in N - type semiconductor.

7. Obtain an expression for density of electrons in the conduction band of an n- type and density of holes in the valence band of a p type extrinsic semiconductor.

8. Obtain an expression for the density of electrons in the conduction band of an n- type semiconductors and show *hat it is proportional to the square root of the donor concentration at low temperatures. Also state what happens at high temperatures. 

9. Obtain an expression for the density of holes in the valence band of p - type semiconductors and show that it is proportional to the square root of the acceptor concentration at low temperatures.

Hall Effect

10. (i) Give the theory of Hall effect.

(ii) Using that effect how will you determine the electrical conductivity of a semiconductor. 

11. (i) What is Hall effect? Derive an expression of Hall coefficient.

(ii) Describe an experimental set-up for the measurement of the Hall voltage and give its applications.

12. (i) What is Hall effect? Show that for a p type semiconductor the Hall coefficient RH is given by 1/pe.

(ii) Mention the applications of Hall effect.

13. What is Hall effect? Give the theory of Hall effect. Describe the Hall effect experiment to determine the Hall coefficient of semiconductor.

14. (i) Obtain expression for Hall coefficient.

(ii) How will you measure Hall coefficient experimentally?

(iii) Describe any two applications of Hall effect.

15. (i) Explain Hall effect in p-type and n-type semiconductors. 

(ii) Derive an expression for Hall coefficient.

(iii) Describe the experimental setup for the measurement of Hall coefficient.

16. What is Hall effect? Derive an expression for Hall coefficient. Describe an experiment for the measurement of the Hall coefficient and mention its applications.

17. (i) Explain the phenomenon of Hall effect.

(ii) Derive an expression for Hall coefficient for a n- type semiconductor and for p - type semiconductor. Also state how Hall voltage is related.

Additional PART B (16 Marks Questions)

1. Derive an expression for electrical conductivity of intrinsic semiconductor.

2. Write down the expression for drift current and diffusion currents.

3. Explain working of any two Hall devices.

4. Describe construction and working of scholtty diode.

5. Write a note on ohmic contact.

ASSIGNMENT PROBLEMS

1. In an intrinsic semiconductor, the effective mass of the electron is 0.07 m。 and that of the hole is 0.4 m where m is the rest mass of the electron. Calculate the intrinsic concentration of charge carriers at 300 K. Given

ER = 0.7 eV.

[Ans: 2.3 × 1018 / m3]

2. In a Hall experiment, a current of 25 A is passed through a long foil of silver which is 0.1 mm thick and 3 cm wide. A magnetic field of flux density 0.14 Wb/m2 is applied perpendicular to the foil. Calculate Hall voltage developed and estimate the mobility of electrons in silver. Given the conductivity of silver is 6.8 × 107 Ω-1 m-1 and Hall coefficient is - 8.4 × 10-11 m3/C.

[Ans: 29.4 μV and μe = 57.7 × 10-4 m2 V-1 s-1]